A spectroscopic census of the Fornax cluster and beyond: preparing for next generation surveys

Maddox, Natasha; Serra, P.; Venhola, Aku; Peletier, Reynier F.; Loubser, S. I.; Iodice, E.

doi:10.1093/mnras/stz2530

Cited by 32 publications

(73 citation statements)

References 54 publications

(60 reference statements)

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“…However, Böhringer et al (2016) also show that this scatter is driven mainly by massive clusters: when their sample is split by the median X-ray luminosity of their associated cluster (corresponding to a total mass of 1.4 × 10 14 M ), the standard deviation in RM increases to 158 ± 34 rad m -2 for sources associated with clusters in the upper half of the mass range and decreases to 62 ± 11 rad m -2 for the converse sources. Our lower derived value of of 16.8 ± 2.4 rad m -2 for the RM scatter seems broadly consistent with this coarse mass dependence, given that the total mass of the Fornax cluster is only 6 +3 −1 × 10 13 M (Drinkwater et al 2001;Nasonova et al 2011;Maddox et al 2019) inside a few Mpc, which is half the mass cut value used by Böhringer et al (2016). It is also comparable to results from simulations for unrelaxed clusters of approximately the same mass (see, e.g.…”

Section: Comparison With Cluster Stacking Experimentssupporting

confidence: 81%

“…The Fornax cluster is nearby (20.64 megaparsecs; Mpc; Lavaux & Hudson 2011), but much poorer than similarly wellstudied clusters like the Virgo and Coma clusters. It has only ∼390 member galaxies (which are typically low in mass; Maddox et al 2019) and has a comparatively low total mass of 6 +3 −1 × 10 13 M (Drinkwater, Gregg & Colless 2001;Nasonova, de Freitas Pacheco, & Karachentsev 2011;Maddox et al 2019), which is one and two orders-of-magnitude less massive than the Virgo and Coma clusters, respectively. The (presently detectable) X-ray-emitting ICM is also small, extending asymmetrically outward from NGC1399 to a mere 15%-30% of the cluster's 1.96 • virial radius.…”

Section: F(φ)e 2iφλ 2 Dφmentioning

confidence: 99%

“…Nevertheless, it is desirable to confirm this for the sources used in our particular RM grid experiment, for reasons described in Section 1. Maddox et al (2019) have compiled a catalogue of reliable spectroscopic redshifts towards the Fornax cluster, drawn from deep optical imaging surveys in the literature as well as their own data. This catalogue is complete within a degree of NGC 1399, down to brightness levels typical of faint ultra-compact dwarf galaxies and globular clusters.…”

Section: Cluster-relative Los Source Positions From Redshift Catalogumentioning

confidence: 99%

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Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

Anderson

Heald

Eilek

et al. 2021

Publ. Astron. Soc. Aust.

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We present the first Faraday rotation measure (RM) grid study of an individual low-mass cluster—the Fornax cluster—which is presently undergoing a series of mergers. Exploiting commissioning data for the POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) covering a ${\sim}34$ square degree sky area using the Australian Square Kilometre Array Pathfinder (ASKAP), we achieve an RM grid density of ${\sim}25$ RMs per square degree from a 280-MHz band centred at 887 MHz, which is similar to expectations for forthcoming GHz-frequency ${\sim}3\pi$ -steradian sky surveys. These data allow us to probe the extended magnetoionic structure of the cluster and its surroundings in unprecedented detail. We find that the scatter in the Faraday RM of confirmed background sources is increased by $16.8\pm2.4$ rad m−2 within 1 $^\circ$ (360 kpc) projected distance to the cluster centre, which is 2–4 times larger than the spatial extent of the presently detectable X-ray-emitting intracluster medium (ICM). The mass of the Faraday-active plasma is larger than that of the X-ray-emitting ICM and exists in a density regime that broadly matches expectations for moderately dense components of the Warm-Hot Intergalactic Medium. We argue that forthcoming RM grids from both targeted and survey observations may be a singular probe of cosmic plasma in this regime. The morphology of the global Faraday depth enhancement is not uniform and isotropic but rather exhibits the classic morphology of an astrophysical bow shock on the southwest side of the main Fornax cluster, and an extended, swept-back wake on the northeastern side. Our favoured explanation for these phenomena is an ongoing merger between the main cluster and a subcluster to the southwest. The shock’s Mach angle and stand-off distance lead to a self-consistent transonic merger speed with Mach 1.06. The region hosting the Faraday depth enhancement also appears to show a decrement in both total and polarised radio emission compared to the broader field. We evaluate cosmic variance and free-free absorption by a pervasive cold dense gas surrounding NGC 1399 as possible causes but find both explanations unsatisfactory, warranting further observations. Generally, our study illustrates the scientific returns that can be expected from all-sky grids of discrete sources generated by forthcoming all-sky radio surveys.

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Section: Comparison With Cluster Stacking Experimentssupporting

confidence: 81%

Section: F(φ)e 2iφλ 2 Dφmentioning

confidence: 99%

Section: Cluster-relative Los Source Positions From Redshift Catalogumentioning

confidence: 99%

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Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

Anderson

Heald

Eilek

et al. 2021

Publ. Astron. Soc. Aust.

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“…We compare our spectra to spectra from the literature (shown in black; see top-left corner for details). We also show the barycentric velocity obtained from our HI spectra (vertical red line) and from optical spectra (vertical blue line; Maddox et al 2019).…”

Section: Flux Density (Jy)mentioning

confidence: 99%

“…In each panel of Fig. 3 we also show the velocity v opt derived from optical spectroscopy (Maddox et al 2019) and the barycentric HI velocity v HI derived from our ATCA spectra.…”

Section: Hi Detection Propertiesmentioning

confidence: 99%

A blind ATCA HI survey of the Fornax galaxy cluster

Loni

Serra

Kleiner

et al. 2021

A&A

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We present the first interferometric blind HI survey of the Fornax galaxy cluster, which covers an area of 15 deg2 out to the cluster virial radius. The survey has a spatial and velocity resolution of 67″ × 95″(∼6 × 9 kpc at the Fornax cluster distance of 20 Mpc) and 6.6 km s−1 and a 3σ sensitivity of NHI ∼ 2 × 1019 cm−2 and MHI ∼ 2 × 107 M⊙, respectively. We detect 16 galaxies out of roughly 200 spectroscopically confirmed Fornax cluster members. The detections cover about three orders of magnitude in HI mass, from 8 × 106 to 1.5 × 1010 M⊙. They avoid the central, virialised region of the cluster both on the sky and in projected phase-space, showing that they are recent arrivals and that, in Fornax, HI is lost within a crossing time, ∼2 Gyr. Half of these galaxies exhibit a disturbed HI morphology, including several cases of asymmetries, tails, offsets between HI and optical centres, and a case of a truncated HI disc. This suggests that these recent arrivals have been interacting with other galaxies, the large-scale potential or the intergalactic medium, within or on their way to Fornax. As a whole, our Fornax HI detections are HI-poorer and form stars at a lower rate than non-cluster galaxies in the same M⋆ range. This is particularly evident at M⋆ ≲ 109 M⊙, indicating that low mass galaxies are more strongly affected throughout their infall towards the cluster. The MHI/M⋆ ratio of Fornax galaxies is comparable to that in the Virgo cluster. At fixed M⋆, our HI detections follow the non-cluster relation between MHI and the star formation rate, and we argue that this implies that thus far they have lost their HI on a timescale ≳1−2 Gyr. Deeper inside the cluster HI removal is likely to proceed faster, as confirmed by a population of HI-undetected but H2-detected star-forming galaxies. Overall, based on ALMA data, we find a large scatter in H2-to-HI mass ratio, with several galaxies showing an unusually high ratio that is probably caused by faster HI removal. Finally, we identify an HI-rich subgroup of possible interacting galaxies dominated by NGC 1365, where pre-processing is likely to have taken place.

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